CVE-2025-27737 is a high-severity vulnerability affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The root cause is improper input validation within the Windows Security Zone Mapping component. This flaw allows an unauthorized local attacker to bypass security features by manipulating input data that the system fails to properly validate. The vulnerability is classified under CWE-20, which pertains to improper input validation, indicating that the system does not correctly verify or sanitize inputs before processing them. Exploitation requires local access and some user interaction but no privileges, making it accessible to low-privileged users or malicious software running on the affected system. The vulnerability has a CVSS v3.1 base score of 8.6, reflecting high impact on confidentiality, integrity, and availability, with a scope change (S:C) indicating that exploitation can affect resources beyond the initially vulnerable component. The attack vector is local (AV:L), and the attack complexity is low (AC:L), meaning the exploit does not require complex conditions. The vulnerability allows an attacker to bypass security zones, potentially enabling execution of malicious code or unauthorized access to sensitive resources that would normally be restricted by zone policies. No known exploits are currently reported in the wild, and no official patches have been linked yet, though the vulnerability was published on April 8, 2025, with a reservation date of March 6, 2025. This vulnerability is significant because Windows Security Zone Mapping is a core security feature that controls how content from different sources (internet, intranet, trusted sites) is handled, and bypassing it can undermine many security controls and lead to privilege escalation or data compromise.

For European organizations, this vulnerability poses a serious risk, especially in environments where Windows 10 Version 1809 is still in use, such as legacy systems or specialized industrial setups. Successful exploitation could allow attackers to bypass security zone restrictions, potentially enabling execution of malicious code or unauthorized access to sensitive data. This can lead to data breaches, disruption of business operations, and compromise of system integrity. Organizations in sectors with strict data protection requirements (e.g., finance, healthcare, government) could face regulatory penalties if this vulnerability is exploited to leak or alter sensitive information. The local attack vector means that insider threats or malware that gains initial foothold could leverage this vulnerability to escalate privileges or move laterally within networks. The scope change indicates that the impact can extend beyond the initially vulnerable component, potentially affecting multiple system components or networked resources. Given the lack of known exploits in the wild, the immediate risk may be moderate, but the high CVSS score and potential impact warrant urgent attention to prevent future exploitation.

1. Immediate mitigation should focus on identifying and isolating systems running Windows 10 Version 1809 (build 10.0.17763.0) within the organization. 2. Apply any available security updates or patches from Microsoft as soon as they are released. Since no patch links are currently provided, monitor official Microsoft security advisories closely. 3. Implement strict local access controls and limit user privileges to reduce the risk of local exploitation. 4. Employ application whitelisting and endpoint protection solutions that can detect or block attempts to exploit security zone bypass techniques. 5. Conduct user awareness training to minimize risky user interactions that could trigger exploitation. 6. Use network segmentation to contain potential lateral movement if a system is compromised. 7. Regularly audit and monitor logs for unusual local activity or security zone policy violations. 8. Consider upgrading affected systems to a supported and patched Windows version if feasible, as Windows 10 Version 1809 is an older release and may no longer receive regular security updates.